This invention relates to thermosetting, solventless polymers containing variable ratios of tungsten, molybdenum or chromium chemically bonded in the polymer chain which have high char yield and which are particularly useful for multi-cycle reimpregnation of a carbon/carbon composite.
With the advent of aerospace products, carbon/carbon composites having high densities have come into widespread use. One or a combination of the following three methods for densification of carbon/carbon composites is commonly employed: (1) high temperature consolidation; (2) chemical vapor deposition; and (3) multi-cycle reimpregnation. For applications involving large parts or complex shapes, multi-cycles reimpregnation has been found to be the most effective method for imparting oxidation resistance and energy absorbing characteristics through the use of specifically formulated polymers.
A reimpregnation resin is a thermosetting polymer introduced as a liquid into the characteristic voids of a carbon/carbon composite. The resin is subsequently cured and heat treated, thus increasing the density of the composite. Selected polymers can be used to impart specific desired characteristics to the composite depending upon the ultimate application. Viable reimpregnation resins must maintain a suitably low viscosity during the reimpregnation process and, in addition, exhibit a relatively high char yield. "Multi-cycle reimpregnation" is the term applied when the reimpregnation process is repeated a number of times.
U.S. Pat. No. 4,185,043 to Robert C. Shaffer discloses thermoplastic and thermosetting polymers which incorporate tungsten and/or molybdenum metal atoms. The metal atoms are incorporated into the polymer by reacting a monomer or polymer containing at least one free carboxyl group with a reaction product of tungsten or molybdenum carbonyl and pyrrolidine to obtain a polymer. It is disclosed that the polymers are useful as reimpregnation resins.